The invention relates to a paint drying system for painted bodies, and particularly, but not exclusively, a system for drying painted motor vehicles.
Conventional automobile spraybooths dry solvent-borne paints which have been applied onto the surfaces of a motor vehicle by passing heated air over the painted surface. Typically, heated air is blown into the spraybooth through inlets e.g. in the booth ceiling and is evacuated through floor outlets.
The surfaces of the bodies such as motor vehicles and particularly non-conductive components such as plastic bumpers, are normally found to be electro-statically charged. This electrostatic charge results from normal handling of the body prior to painting and is generally unavoidable.
The electrostatically charged surfaces of the vehicle attract dirt and dust particles and this results in contamination of the painted surface.
In an attempt to reduce such contamination, the surface is typically degreased and xe2x80x9ctacked offxe2x80x9d (rubbed using what is commonly referred to as a xe2x80x9ctack ragxe2x80x9d) prior to painting. However, this can be counter-productive as the rubbing action greatly increases the static charge on the surface. Loose/airborne particles originating from tack cloths, operator clothing etc., are then attracted to the surface.
Paint is typically applied to motor vehicles using a spray gun. When the paint is atomised from the spray gun, this also acquires a static charge which attracts dirt and dust particles.
The result is that the painted surface is often contaminated by dust/dirt particles and although the painting process is designed for a xe2x80x9cgun finishxe2x80x9d without subsequent polishing, refinishing work is often necessary involving many wasted hours of removing dirt ingressed during painting which reduces the cost effectiveness of the painting operation.
A further problem is that metallic paint finishes make up approximately 50% of car colours currently on the road. Mica or aluminium is used to produce the metallic finish and is disturbed by static charge which can result in a patchy surface and colour inaccuracy.
It is, therefore, an object of this invention to provide a system for drying a painted body which eliminates or, at least, reduces contamination by dust and particles of the painted surface, thereby eliminating or, at least, reducing the need for refinishing operations.
According to the invention therefore there is provided a paint drying system for drying a painted body, the system comprising a spraybooth having an enclosure, an air inlet, an air outlet and means to supply air to the inlet to flow through the enclosure from the inlet to the outlet, characterised by the provision of means for electrically charging the said air supply.
With this arrangement any static charge on the body surfaces or on particles present on the surfaces is neutralised by ions in the air supplied, thereby eliminating or, at least reducing contamination of painted surfaces and eliminates or reduces the need for refinishing operations which would otherwise reduce the cost effectiveness of the operation.
A further, somewhat surprising effect, which has been noted is a reduction by 20% in drying times of painted motor vehicles.
Furthermore, it has been found that dust and dirt particles are predominantly positively charged.
Thus, preferably the supply air is negatively charged. The negative ions produced neutralise any positively charged particles present on the panel thereby neutralising the attractive forces between the charged contaminants and the panel so that the contaminants are then easily blown off the surface by the air flow through the booth and subsequently removed via the air outlet.
However, it is not intended that the invention is to be restricted to the negative ionisation, and it is envisaged that positive ionisation may be provided, if desired, for example, to neutralise contaminants found to be negatively charged.
The means for electrically charging the air inlet supply to the enclosure may take any suitable form however and this preferably comprises at least one ionisation member operable to be electrically charged by, for example, appropriate electrical coupling to a voltage supply.
The each ionisation member preferably comprises a conductive material e.g. metal.
Alternative forms of air charging means may be used, however, the advantage of using a high voltage charging device is that this type of device is not regulated by stringent legislation and is fairly easy and inexpensive to obtain. Furthermore, a high voltage charging device can be safely used whilst operators are inside the enclosure.
The spraybooth may take any suitable form but, preferably, the means to supply air to the inlet comprises a pump/pumps, which preferably are operable to supply air from the atmosphere externally of the booth to the air inlet. Preferably, also the spraybooth incorporates a heater for heating the inlet air.
Alternatively, air may be re-circulated from within the enclosure, or from a plenum chamber of the inlet or outlet air system.
The air inlet may take any suitable form and may include a duct/duct system which is connected to the enclosure at one or more openings in the enclosure walls or ceilings etc. so as to supply air into the enclosure.
The spraybooth may have at least one further air inlet which may receive air from the atmosphere externally of the booth and direct this air into the enclosure transversely of the said airflow.
Alternatively, this air may be re-circulated from the enclosure to the further air inlet.
This air inlet may comprise air nozzles or jets which are mounted internally of the enclosure and are operable to direct air obliquely at surfaces of the body.
The air nozzles/jets may be mounted on a housing or support structure which is mounted internally of the enclosure.
Compressed air may be supplied to the air inlet and/or the further air inlet by means of an air compression device.
The or each ionisation member may be located in any suitable position. However, preferably the or each ionisation member is mounted internally of the enclosure and particularly, preferably, directly in the path of the air flow into the enclosure, from the air inlet and/or the further air inlet.
To this end, the ionisation member may be mounted on an internal structure of the enclosure e.g. wall, ceiling, etc., and preferably adjacent e.g., so as to straddle the or each enclosure opening.
With this arrangement, ions produced by the or each ionisation member may be distributed to the body surfaces by the said air flow (from the inlet).
However, the invention is not intended to be restricted to mounting of the ionisation member within the enclosure. Alternatively, the ionisation member may be located at any suitable position within the air inlet and/or the further air inlet.
Where the spraybooth incorporates a further air inlet, as mentioned above, the or each or any ionisation member may be attached to, or adjacent, the further air inlet, so as to position the member directly in the path or the air flow from the nozzles/jets into the enclosure. Alternatively, there may be one or more ionisation members within or adjacent each jet or nozzle.
The or each further air inlet may include doors which, in a closed position, are operable to shield or enclose the nozzles or jets when not in use e.g. during painting so as to prevent contamination of the nozzles/jets by airborne paint particles.
The or each ionisation member may be located so as to be shielded or enclosed by the doors when in a closed position.
The or each ionisation member may be mounted so as to be positionally adjustable.
The or each ionisation member may have any suitable structure, and may be an elongate bar or rod or a grid/grill structure.
Preferably, the or each further air inlet comprises one or more parallel columns of nozzles/jets and there is one ionisation member consisting an elongate metal rod which is mounted generally parallel with the said columns.
The ionisation member may be integral to the spraybooth so that part of the spraybooth is electrically charged.
Advantageously, the paint drying system may also be used for drying a body painted with a water-based paint.
The body may be any suitable body, but preferably, it is a motor vehicle.
A further problem concerns a control system for controlling a paint drying system.
Conventional automobile paint drying systems comprise a spraybooth in which the motor vehicle body is first painted and then dried (or xe2x80x98bakedxe2x80x99). The temperature at which the painted body must be dried and the drying time is critically dependent upon the type of paint which has been applied and the paint surface finish required.
Spraybooth drying times are generally the most important factor within a busy paint spraying workshop. Each paint product has optimum drying temperature time (collectively referred to as a drying cycle) both in terms of speed and quality. The same applies to paint manufacturers as a paint product as one company may benefit from different temperature profile to that of another manufacturer.
Spraybooth operator errors in setting the temperature and time of the drying process can mean that the paint is not dried sufficiently, and in this case, the drying process must be repeated in its entirety. Such errors may expensively reduce the number of painted bodies which may be dried and so reduce the cost effectiveness of the paint drying operation.
A further object of the present invention is to provide a control system which eliminates or reduces operator error.
According to a further aspect the invention therefore, there is provided a control system for controlling a paint drying system for drying a painted body, the control system including at least one user-operable control, the or each user operable control being operable to preselect a predetermined parameter or predetermined combination of parameters.
With this arrangement the paint drying system can be operated in a quick and efficient manner, increasing the throughput of the paint drying system and, at the same time because individual setting of the various system parameters is not necessary, there is less risk of user error when operating the paint drying system.
The painted body is preferably a motor vehicle, e.g. a motor car. However the invention may also advantageously used for drying other painted bodies such as aircraft bodies, watercraft bodies etc.
The paint drying system may include a spraybooth which may have an enclosure in which the painted body is dried. The spraybooth may have an air inlet and air outlet, and pump means to supply air from atmosphere externally of the spraybooth to the air inlet to flow through the enclosure from the air inlet to the air outlet. Preferably, the spray booth incorporates a heater for heating the inlet air.
The or each user-operable control may be operable to preselect a single predetermined parameter, such as temperature.
However, the or each user-operable control may be operable to control any number and combination of system parameters, such as inlet air flow rate, temperature, pressure, humidity, spraybooth enclosure temperature, pressure, humidity, etc.
The control system may incorporate sensors for sensing paint drying system operating parameter values, such a enclosure temperature, pressure, inlet flow rate etc., so that such parameter values can be monitored and regulated by the control system.
Preferably, the or each user-operable control is operable to preselect at least two predetermined parameters, wherein one of such parameters is a time and/or temperature related parameter.
Most preferably, the or each user-operable control is operable to control the characteristics of a respective drying stage or cycle in which a parameter such a temperature, or combination of parameters vary with time.
The spraybooth may have at least one further air inlet which receives air from the atmosphere externally of the booth and directs this air into the enclosure transversely to said air flow.
This air inlet may comprise air nozzles or jets which are mounted internally of the enclosure and are operable to direct air obliquely at surfaces of the motor vehicle.
Accordingly, the user-operable control may be operable to preselect system parameters associated with the further air inlet airflow, such as air flow rate, temperature, pressure, humidity etc.
The predetermined parameters which are preselected by the or each user-operable control may vary with respect to time, such that the parameter values vary during a particular drying stage or cycle. For instance, a parameter may increase/decrease incrementally throughout the drying cycle or part of the cycle, or there may be one or more ramped increase/decrease(s) during a cycle.
In a preferred embodiment there are a plurality of user-operable controls, each control being operable to preselect the parameters of an associated drying cycle, such that a plurality of drying cycles may be provided for.
The or each user operable control may take any suitable form and may comprise a button, key, switch, touch/heat/photo-sensitive display screen etc.
Preferably, the control system incorporates an electronic control unit such as programmable controller or a microprocessor based unit and may further incorporate a data storage (memory) unit so that the parameter values may be stored.
Preferably the control unit is pre-programmable so that the system parameters for the or each drying cycle of the system may be pre-programmed, by , for example, the spraybooth proprietor, or manufacturer.
Accordingly, the control unit may include a data entry device such as a keypad or keyboard and further preferably a date entry display device to enable viewing of entered programming data during and/or after pre-programming.
The control system may incorporate a display device to display the parameter settings of a particular drying cycle. This display device may be operative to display the parameter settings either on demand and/or during a drying cycle.
The or each display may comprise any suitable form but preferably incorporates a digital display. There may be a separate display for each of the above functions or alternatively, and preferably there is a single, multi-functional display device operative to display parameter values during pre-programming and during a drying cycle.
Preferably, the control system includes a housing which houses the above described control system components. The housing may take any suitable form such as a metal or plastic box construction.
The housing may be attached or integral to the spraybooth, but preferably, it provides for electrical/pneumatic/hydraulic coupling of the control system to corresponding spraybooth components as is required e.g. an electric coupling between the or each heater, a spraybooth thermo-sensor and the control housing for effecting enclosure temperature control; a pneumatic coupling between a pressure sensor in the enclosure interior and the control housing and any of the spraybooth flow rate devices (pumps, fans, flow dampers etc.) for effecting control of the pressure of the enclosure etc.
Preferably, the user operable components of the control system including the user operable control(s), data entry device(s) and any display device(s) alarms etc., are mounted so as to be accessible by a user/operator when outside of the enclosure.
Advantageously, these user operable components mentioned above are mounted on a panel which may be incorporated into the above described housing.